DESCRIPTION

Each of these functions has the same behavior as its counterpart
without the "_unlocked" suffix, except that they do not use locking
(they do not set locks themselves, and do not test for the presence of
locks set by others) and hence are thread-unsafe. See flockfile(3).

CONFORMINGTO

The four functions getc_unlocked(), getchar_unlocked(),
putc_unlocked(), putchar_unlocked() are in POSIX.1-2001.
The nonstandard *_unlocked() variants occur on a few Unix systems, and
are available in recent glibc. They should probably not be used.